Smithers
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Smithers clear sky chart from 2005-11-06 to 2024-03-23.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	11% 12% 5% 10% 9% 5% 6% 6% 6% 7% 22%	78334
	Night	10% 14% 6% 11% 9% 5% 6% 6% 6% 7% 21%	81494
Transparency	Day	57% 10% 13% 15% 4	78032
	Night	57% 11% 13% 14% 4 1	81376
Seeing	Day	18% 13% 25% 26% 14% 4	15471
	Night	16% 9% 23% 33% 17% 2	23259

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	9% 17% 8% 19% 16% 5% 6% 5% 4 4 6%	2219
	11th to 20th	Day	8% 16% 6% 12% 9% 5% 6% 6% 6% 8% 18%	2199
	21st to end	Day	15% 24% 8% 15% 8% 3 6% 4 5% 4 8%	2442
February	1st to 10th	Day	10% 13% 8% 14% 10% 4 7% 6% 5% 5% 17%	1510
	11th to 20th	Day	5% 15% 7% 8% 8% 5% 7% 6% 7% 7% 26%	1627
	21st to end	Day	4 13% 6% 11% 10% 5% 8% 5% 5% 6% 25%	1413
March	1st to 10th	Day	5% 15% 7% 12% 12% 5% 6% 5% 6% 5% 22%	1895
	11th to 20th	Day	6% 14% 7% 10% 8% 4 7% 7% 8% 8% 20%	2090
	21st to end	Day	8% 15% 6% 11% 10% 5% 7% 5% 6% 6% 22%	2201
April	1st to 10th	Day	9% 16% 6% 13% 10% 5% 6% 6% 6% 6% 19%	2290
	11th to 20th	Day	8% 18% 7% 11% 10% 5% 6% 5% 6% 6% 20%	2308
	21st to end	Day	12% 14% 6% 9% 9% 5% 7% 5% 6% 7% 21%	2384
May	1st to 10th	Day	12% 13% 5% 9% 7% 4 6% 5% 5% 7% 27%	2664
	11th to 20th	Day	13% 11% 5% 10% 8% 4 6% 6% 6% 8% 23%	2656
	21st to end	Day	15% 10% 5% 9% 8% 4 6% 5% 5% 7% 25%	2917
June	1st to 10th	Day	15% 10% 5% 10% 9% 5% 7% 6% 5% 6% 22%	2783
	11th to 20th	Day	13% 10% 5% 9% 7% 5% 6% 6% 6% 8% 26%	3024
	21st to end	Day	13% 8% 5% 9% 8% 4 7% 6% 6% 7% 27%	3027
July	1st to 10th	Day	10% 6% 3 8% 9% 5% 8% 6% 7% 8% 31%	2819
	11th to 20th	Day	11% 8% 5% 8% 8% 3 7% 6% 6% 8% 30%	2700
	21st to end	Day	9% 7% 4 8% 8% 4 7% 7% 7% 8% 33%	2938
August	1st to 10th	Day	8% 5% 3 8% 7% 4 6% 7% 6% 8% 39%	2679
	11th to 20th	Day	10% 7% 3 5% 6% 3 6% 6% 7% 8% 38%	2363
	21st to end	Day	15% 10% 5% 10% 9% 4 5% 6% 6% 6% 24%	2574
September	1st to 10th	Day	14% 10% 4 9% 9% 4 5% 5% 6% 7% 25%	2300
	11th to 20th	Day	14% 10% 4 8% 8% 4 6% 6% 6% 6% 27%	2005
	21st to end	Day	18% 13% 4 10% 7% 5% 7% 6% 6% 7% 18%	1980
October	1st to 10th	Day	15% 13% 4 8% 9% 4 6% 5% 6% 7% 23%	1827
	11th to 20th	Day	15% 14% 5% 10% 8% 5% 8% 6% 7% 8% 14%	1679
	21st to end	Day	15% 14% 5% 9% 6% 3 7% 5% 6% 6% 22%	1701
November	1st to 10th	Day	15% 15% 6% 11% 10% 5% 6% 6% 6% 5% 16%	1488
	11th to 20th	Day	11% 16% 8% 13% 11% 5% 7% 6% 5% 5% 13%	1368
	21st to end	Day	10% 16% 6% 13% 10% 5% 8% 8% 5% 6% 12%	1330
December	1st to 10th	Day	8% 12% 5% 13% 13% 7% 7% 9% 6% 7% 15%	1178
	11th to 20th	Day	10% 21% 7% 13% 11% 5% 6% 5% 5% 6% 12%	1442
	21st to end	Day	9% 15% 7% 14% 12% 6% 8% 7% 6% 6% 10%	2314
January	1st to 10th	Night	10% 22% 9% 18% 12% 4 6% 5% 3 4 7%	4726
	11th to 20th	Night	9% 17% 6% 10% 8% 4 6% 5% 6% 7% 22%	4699
	21st to end	Night	16% 23% 8% 14% 9% 4 5% 5% 4 4 8%	5214
February	1st to 10th	Night	10% 17% 6% 12% 10% 5% 5% 5% 5% 5% 18%	2669
	11th to 20th	Night	7% 14% 5% 11% 8% 4 6% 6% 6% 8% 24%	2440
	21st to end	Night	5% 12% 5% 10% 9% 5% 7% 6% 7% 7% 28%	2041
March	1st to 10th	Night	5% 13% 7% 10% 7% 5% 7% 6% 7% 7% 24%	2283
	11th to 20th	Night	4 13% 6% 10% 9% 6% 7% 7% 7% 7% 23%	2089
	21st to end	Night	7% 15% 7% 10% 8% 4 6% 7% 6% 7% 24%	2200
April	1st to 10th	Night	8% 11% 4 10% 9% 5% 7% 8% 6% 7% 25%	1668
	11th to 20th	Night	6% 15% 6% 11% 8% 4 6% 6% 7% 8% 24%	1601
	21st to end	Night	9% 14% 5% 9% 9% 4 7% 5% 5% 6% 26%	1575
May	1st to 10th	Night	9% 10% 6% 9% 6% 4 5% 6% 6% 9% 29%	1295
	11th to 20th	Night	12% 9% 4 7% 5% 4 7% 7% 7% 10% 29%	1239
	21st to end	Night	13% 9% 3 7% 6% 4 6% 6% 8% 8% 30%	1358
June	1st to 10th	Night	11% 10% 5% 6% 7% 5% 6% 7% 6% 8% 29%	1175
	11th to 20th	Night	8% 7% 4 7% 6% 2 7% 6% 9% 10% 35%	932
	21st to end	Night	10% 6% 4 7% 6% 5% 6% 7% 8% 11% 31%	928
July	1st to 10th	Night	10% 5% 2 7% 7% 4 6% 6% 6% 11% 37%	1138
	11th to 20th	Night	9% 7% 3 5% 7% 3 5% 6% 8% 9% 39%	1260
	21st to end	Night	5% 5% 2 6% 6% 6% 7% 7% 7% 10% 39%	1379
August	1st to 10th	Night	7% 4 3 5% 5% 3 5% 6% 6% 8% 49%	1257
	11th to 20th	Night	8% 6% 2 6% 6% 3 5% 5% 7% 7% 46%	1536
	21st to end	Night	13% 7% 3 8% 8% 4 5% 6% 7% 8% 31%	1782
September	1st to 10th	Night	14% 8% 4 7% 8% 4 5% 5% 4 7% 35%	1659
	11th to 20th	Night	9% 8% 3 8% 7% 5% 6% 6% 7% 6% 35%	1952
	21st to end	Night	15% 10% 5% 9% 8% 5% 6% 7% 7% 7% 22%	1980
October	1st to 10th	Night	15% 10% 4 9% 6% 4 5% 5% 6% 6% 29%	2132
	11th to 20th	Night	16% 14% 4 9% 8% 5% 7% 6% 7% 6% 18%	2279
	21st to end	Night	13% 14% 6% 9% 8% 4 6% 6% 7% 8% 21%	2654
November	1st to 10th	Night	15% 14% 6% 11% 9% 6% 7% 6% 6% 7% 15%	2590
	11th to 20th	Night	9% 19% 7% 12% 9% 5% 6% 6% 6% 7% 14%	2812
	21st to end	Night	8% 17% 8% 14% 10% 6% 7% 6% 5% 6% 13%	2850
December	1st to 10th	Night	7% 12% 7% 12% 13% 7% 7% 6% 8% 7% 15%	2982
	11th to 20th	Night	10% 17% 8% 14% 11% 4 6% 6% 5% 5% 12%	3750
	21st to end	Night	7% 17% 8% 15% 12% 6% 7% 6% 6% 5% 10%	5370

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	68% 18% 8% 5% 2	2219
	11th to 20th	Day	62% 7% 13% 6% 7% 5%	2220
	21st to end	Day	74% 11% 6% 6% 2 1	2442
February	1st to 10th	Day	64% 10% 7% 9% 9% 1	1510
	11th to 20th	Day	52% 12% 15% 15% 6%	1636
	21st to end	Day	56% 8% 11% 17% 6% 2	1413
March	1st to 10th	Day	59% 9% 11% 15% 6% 1	1895
	11th to 20th	Day	54% 10% 14% 16% 5%	2090
	21st to end	Day	60% 9% 14% 14% 3	2201
April	1st to 10th	Day	61% 10% 11% 15% 3	2290
	11th to 20th	Day	63% 6% 11% 15% 5%	2308
	21st to end	Day	60% 8% 12% 14% 6%	2384
May	1st to 10th	Day	56% 8% 14% 17% 5%	2664
	11th to 20th	Day	57% 8% 12% 17% 5% 1	2659
	21st to end	Day	57% 7% 14% 18% 5%	2918
June	1st to 10th	Day	59% 8% 13% 14% 5%	2783
	11th to 20th	Day	53% 8% 16% 19% 4	3024
	21st to end	Day	53% 10% 16% 17% 3	3027
July	1st to 10th	Day	48% 10% 16% 21% 4	2743
	11th to 20th	Day	50% 11% 19% 17% 3	2619
	21st to end	Day	43% 12% 19% 21% 5%	2775
August	1st to 10th	Day	39% 10% 20% 24% 6%	2661
	11th to 20th	Day	39% 13% 20% 22% 6%	2363
	21st to end	Day	57% 11% 16% 13% 3 1	2574
September	1st to 10th	Day	55% 11% 15% 16% 2	2300
	11th to 20th	Day	52% 10% 16% 19% 3 1	2005
	21st to end	Day	63% 10% 13% 11% 4	1980
October	1st to 10th	Day	56% 11% 15% 13% 5%	1827
	11th to 20th	Day	63% 13% 14% 7% 2	1679
	21st to end	Day	59% 10% 13% 16% 3	1701
November	1st to 10th	Day	66% 9% 11% 12% 2	1488
	11th to 20th	Day	70% 9% 9% 9% 4	1368
	21st to end	Day	65% 13% 11% 8% 3	1330
December	1st to 10th	Day	61% 14% 10% 11% 3	1178
	11th to 20th	Day	67% 11% 7% 11% 3	1444
	21st to end	Day	62% 17% 7% 9% 5%	2314
January	1st to 10th	Night	74% 13% 6% 5% 1	4726
	11th to 20th	Night	59% 7% 12% 8% 9% 5%	4740
	21st to end	Night	71% 15% 6% 5% 3	5214
February	1st to 10th	Night	63% 10% 8% 10% 9% 1	2669
	11th to 20th	Night	54% 9% 14% 16% 6%	2442
	21st to end	Night	50% 10% 12% 20% 8% 1	2041
March	1st to 10th	Night	50% 11% 13% 17% 8% 1	2283
	11th to 20th	Night	54% 12% 12% 17% 5%	2090
	21st to end	Night	56% 9% 14% 17% 4	2200
April	1st to 10th	Night	52% 11% 14% 16% 6%	1668
	11th to 20th	Night	54% 9% 14% 19% 5%	1601
	21st to end	Night	56% 7% 13% 18% 5%	1575
May	1st to 10th	Night	48% 10% 18% 20% 4	1295
	11th to 20th	Night	49% 9% 20% 16% 6% 1	1239
	21st to end	Night	49% 9% 17% 22% 3	1358
June	1st to 10th	Night	49% 9% 17% 21% 4 1	1175
	11th to 20th	Night	41% 13% 18% 23% 6%	932
	21st to end	Night	44% 10% 21% 21% 4	928
July	1st to 10th	Night	40% 11% 20% 24% 4 1	1105
	11th to 20th	Night	39% 12% 25% 21% 4	1218
	21st to end	Night	36% 13% 25% 19% 6%	1302
August	1st to 10th	Night	30% 11% 25% 29% 6%	1250
	11th to 20th	Night	34% 11% 25% 26% 5%	1536
	21st to end	Night	48% 11% 19% 19% 2	1782
September	1st to 10th	Night	47% 11% 20% 19% 3	1659
	11th to 20th	Night	44% 10% 19% 22% 5%	1952
	21st to end	Night	57% 14% 11% 14% 4	1980
October	1st to 10th	Night	52% 9% 17% 17% 5%	2132
	11th to 20th	Night	61% 12% 14% 10% 2	2279
	21st to end	Night	55% 13% 13% 15% 4	2654
November	1st to 10th	Night	65% 11% 10% 12% 2	2590
	11th to 20th	Night	65% 11% 10% 11% 2	2812
	21st to end	Night	67% 11% 8% 10% 3	2850
December	1st to 10th	Night	61% 12% 12% 11% 4	2982
	11th to 20th	Night	68% 9% 9% 10% 3	3747
	21st to end	Night	64% 16% 7% 8% 5%	5370

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 11% 22% 32% 17% 2	180
	11th to 20th	Day	22% 11% 21% 26% 14% 7%	180
	21st to end	Day	15% 16% 17% 37% 12% 4	198
February	1st to 10th	Day	18% 16% 26% 25% 13% 3	360
	11th to 20th	Day	15% 13% 27% 32% 11% 2	365
	21st to end	Day	16% 14% 30% 26% 9% 6%	307
March	1st to 10th	Day	14% 19% 26% 23% 14% 5%	377
	11th to 20th	Day	14% 15% 29% 25% 14% 3	460
	21st to end	Day	21% 14% 24% 25% 12% 4	471
April	1st to 10th	Day	21% 14% 29% 20% 12% 3	420
	11th to 20th	Day	18% 14% 25% 22% 16% 5%	412
	21st to end	Day	20% 21% 25% 20% 9% 4	420
May	1st to 10th	Day	21% 13% 28% 25% 10% 3	567
	11th to 20th	Day	18% 15% 21% 27% 14% 5%	625
	21st to end	Day	19% 15% 27% 26% 10% 4	680
June	1st to 10th	Day	20% 14% 26% 24% 13% 2	713
	11th to 20th	Day	14% 13% 30% 27% 13% 2	810
	21st to end	Day	14% 9% 25% 30% 17% 4	777
July	1st to 10th	Day	14% 12% 25% 29% 15% 5%	621
	11th to 20th	Day	14% 12% 27% 26% 17% 4	618
	21st to end	Day	13% 9% 30% 29% 15% 4	684
August	1st to 10th	Day	11% 11% 25% 30% 15% 8%	626
	11th to 20th	Day	17% 12% 28% 23% 16% 4	502
	21st to end	Day	21% 14% 25% 20% 15% 4	495
September	1st to 10th	Day	24% 14% 23% 22% 14% 4	450
	11th to 20th	Day	19% 14% 17% 24% 19% 7%	450
	21st to end	Day	26% 13% 27% 19% 12% 2	450
October	1st to 10th	Day	26% 14% 20% 20% 16% 5%	450
	11th to 20th	Day	24% 15% 26% 21% 12% 3	390
	21st to end	Day	24% 14% 22% 25% 12% 3	315
November	1st to 10th	Day	28% 14% 14% 30% 8% 6%	180
	11th to 20th	Day	23% 7% 16% 26% 23% 4	180
	21st to end	Day	24% 12% 15% 25% 18% 6%	180
December	1st to 10th	Day	13% 6% 15% 39% 21% 6%	180
	11th to 20th	Day	14% 7% 18% 37% 19% 4	180
	21st to end	Day	15% 5% 16% 39% 18% 7%	198
January	1st to 10th	Night	17% 11% 26% 34% 11% 1	850
	11th to 20th	Night	17% 12% 25% 34% 11% 2	850
	21st to end	Night	19% 13% 23% 30% 13% 2	935
February	1st to 10th	Night	16% 12% 27% 29% 14% 1	850
	11th to 20th	Night	15% 7% 24% 40% 13% 2	762
	21st to end	Night	11% 10% 24% 38% 15% 2	628
March	1st to 10th	Night	10% 13% 25% 30% 19% 2	760
	11th to 20th	Night	11% 13% 25% 35% 15% 2	760
	21st to end	Night	16% 10% 21% 28% 22% 4	800
April	1st to 10th	Night	13% 9% 22% 30% 22% 4	550
	11th to 20th	Night	14% 10% 22% 29% 23% 3	533
	21st to end	Night	17% 9% 25% 29% 20% 1	495
May	1st to 10th	Night	13% 8% 22% 38% 18% 1	360
	11th to 20th	Night	14% 6% 19% 36% 23% 3	354
	21st to end	Night	16% 7% 21% 35% 20% 1	389
June	1st to 10th	Night	15% 6% 17% 39% 21% 1	360
	11th to 20th	Night	11% 5% 28% 39% 17% 1	360
	21st to end	Night	13% 6% 19% 43% 19% 1	360
July	1st to 10th	Night	11% 6% 22% 39% 21% 1	350
	11th to 20th	Night	13% 4 20% 39% 22% 2	348
	21st to end	Night	6% 4 20% 48% 21% 2	394
August	1st to 10th	Night	10% 5% 15% 33% 37% 1	362
	11th to 20th	Night	11% 4 23% 35% 25% 3	534
	21st to end	Night	17% 5% 18% 37% 21% 1	594
September	1st to 10th	Night	18% 8% 19% 33% 19% 2	579
	11th to 20th	Night	13% 7% 19% 31% 25% 5%	720
	21st to end	Night	20% 9% 23% 31% 14% 3	720
October	1st to 10th	Night	23% 10% 18% 30% 18% 3	720
	11th to 20th	Night	24% 10% 18% 32% 15% 2	720
	21st to end	Night	23% 9% 23% 32% 13% 1	792
November	1st to 10th	Night	23% 11% 27% 24% 13% 2	740
	11th to 20th	Night	19% 11% 26% 31% 11% 2	832
	21st to end	Night	18% 10% 28% 29% 14% 2	850
December	1st to 10th	Night	13% 9% 23% 37% 16% 3	982
	11th to 20th	Night	14% 9% 25% 36% 14% 2	1040
	21st to end	Night	15% 9% 25% 36% 13% 2	1026

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